Above table students is user table however -ROOT- and .META. are HBase catalog tables. These tables are part of HBase configuration where HBase keeps catalog about the user tables. To understand each table structure lets run describe command:

Usage:
[–input <input> –output <output> –distanceMeasure <distanceMeasure>
–clusters <clusters> –numClusters <k> –convergenceDelta <convergenceDelta>
–maxIter <maxIter> –overwrite –clustering –method <method>
–outlierThreshold <outlierThreshold> –help –tempDir <tempDir> –startPhase
<startPhase> –endPhase <endPhase>]
–clusters (-c) clusters The input centroids, as Vectors. Must be a
SequenceFile of Writable, Cluster/Canopy. If k is
also specified, then a random set of vectors will
be selected and written out to this path first